This invention relates to a data recording and reproducing apparatus and method, and more particularly to an apparatus and method for writing data on and reading data from an optical disk by illuminating the disk with a light beam while the disk is rotating.
An optical disk which is a medium for mass data storage is currently attracting much attention. The disk is used in, for example, an image information filing system. In the system, the recording surface of the disk is illuminated with a laser beam while the disk is spinning, whereby image information is recorded on or reproduced from the disk. During recording, image information is converted into digital data and the digital data are subjected to pulse-width modulation, thus providing pulse-width-modulated signals. A recording beam, or a high-energy laser beam, is intermittently applied on the recording surface of the optical disk in accordance with the pulse-width-modulated signals. The recording beam produces pits of varying lengths along a spiral or circular track on the disk. During reproduction, a reproducing beam, or a low-energy laser beam, is applied on the track. The portion of the reproducing beam reflected from the track is converted into image signals by a photosensor of an optical head.
If an optical disk unit is used in an image information filing system, it must be made small, light, inexpensive and easy to operate. An optical disk unit which fulfills all these requirements cannot perform data recording or data reproduction with high precision, however. This is because, for example, a focussing operation of the optical head is not stable and also the optical disk warps and has no uniform light-sensitivity. It is therefore difficult to form pits of uniform size in the recording surface of the disk. If a reproducing beam is not correctly focused on the track, image signals corresponding to the beam reflected from the track will be erroneous and the data reproduced from the image signals will be incorrect.